In recent years, there is a rapid tendency to mount touch panels on various electronic devices, for example, information devices such as smartphones or vending machines such as ticket vending machines. Recently, a capacitive type touch panel is widely used because of its capability of accepting multi-touch.
The capacitive type touch panel includes (i) a plurality of X sensor electrodes and (ii) a plurality of Y sensor electrodes arranged so as to be orthogonal to the X sensor electrodes in a plan view. According to the capacitive type touch panel, drive signals are supplied to the Y sensor electrodes and sense signals are taken from the X sensor electrodes, so that capacitances formed between the X sensor electrodes and the Y sensor electrodes are detected. Based on amounts of changes in the capacitances, it is possible to calculate a position of a detection target on a detection surface.
In a case where (i) disconnection of a sensor electrode (hereinafter, the term “sensor electrode” refers to the X sensor electrode and/or the Y sensor electrode) occurs or (ii) a short circuit (leakage) occurs between sensor electrodes, it is impossible to detect a capacitance between the sensor electrodes, and thus it is impossible to calculate the position of the detection target. In order to deal with this, an inspection step of inspecting whether or not the touch panel operates normally is required.
According to a conventional inspection step, (i) a contact probe is used for inspecting conductivity of sensor electrodes arranged on a sensor substrate, and (ii) in a case where a disconnection or a short circuit is found in the sensor electrodes as a result of the inspection, the sensor substrate is determined to be defective.
However, although the above conventional inspection method is able to determine whether or not the sensor substrate is defective according to the presence or absence of the disconnection or short circuit of the sensor electrodes, the above conventional inspection method is not able to accurately detect a widened or thinned sensor electrode. Despite the fact that the widened or thinned sensor electrode greatly affects detection accuracy of the touch panel, the conventional inspection method is not able to accurately detect the widened or thinned sensor electrode. Further, for example, in a case of performing, according to the conventional inspection method, an inspection on a sensor substrate including (i) sensor electrodes arranged in a diamond pattern and (ii) dummy electrodes each provided, as a floating electrode, between adjacent ones of the sensor electrodes, it is necessary to bring the contact probe into contact with each of the dummy electrodes in order to examine the presence or absence of leakage between the dummy electrode and its respective sensor electrode. This results in a time-consuming inspection process.
Patent Literature 1 discloses an inspection method including (i) causing an inspection jig which includes inspection electrodes to face an inspection target sample (sensor module) which includes first sensor electrodes and second sensor electrodes orthogonal to each other, (ii) changing electric potentials of the inspection electrodes to a given fixed value so as to so as to simulate a state where the sensor module is touched by an inspection target, and (iii) detecting a defect caused by, e.g., disconnection of a sensor electrode according to an amount of change in a capacitance between the sensor module and the inspection jig.
With the above inspection method, it is possible to perform inspections without determination variations among different inspections.